Conventionally, various film antennas to be used while being installed to a glass face of an automobile have been proposed with the popularization of car navigation systems.
A film antenna is attached to a fixed glass face. However, since heating lines for a defogger are generally wired in rear glass, the film antenna is often attached to front glass to avoid interference with the heating lines.
As this kind of film antenna, there have been proposed (a) those which are obtained by forming an antenna pattern with a metal thin wire on a transparent plastic film with electrical isolation, and (b) those which have transparency by forming a large number of fine holes on a metal foil to be an antenna by punching or the like.
However, the film antennas described in (a) have a problem that the bent metal thin wire is seen outstandingly from the inside or the outside of an automobile to not only worsen the design but also become an obstacle in driver's visibility, because of the configuration of bending and curving the wire in the antenna shape and sticking the metal thin wire to a transparent plastic film.
Further, the film antenna described in (b) is seen more outstandingly as compared with the film antenna described in (a) since a large number of holes are formed on a metal foil by punching. Moreover, whether the design of the antenna is good or bad depends on the punching accuracy of the punched holes.
If an antenna pattern is constructed from a transparent electrically conductive film used for a touch panel or the like, it is expected that an excellent design and a good driver's visibility can be assured as compared with the film antennas described in (a) and (b).
However, the transparent electrically conductive film has a characteristic that as the film thickness is made thinner and the transparency is increased more, the surface resistance, which is a measure of the conductivity, is increased more and it is therefore difficult to provide the transparency required for front glass and low resistance required for the antenna.
Incidentally, the resistance of a transparent electrically conductive film whose transparency is assured has a resistance of several tens to several hundreds Ω, meanwhile the resistance required for the antenna has to be a value as low as 3Ω or lower.
The present invention has been accomplished in consideration of the above-mentioned problems of conventional film antennas and an object of the present invention is to provide a transparent antenna for a vehicle having transparency for giving a good driver's visibility without worsening the design of the antenna and capable of realizing low resistance required for the antenna as well as vehicle glass with an antenna.